Wireless communication devices, such as WIFI 802.11N and LTE compliant communication devices, are increasingly using MIMO antenna technology to provide increased data communication rates with decreased error rates. A MIMO antenna includes at least two antenna elements. The operational performance of a MIMO antenna depends upon obtaining sufficient decoupling and decorrelation between its antenna elements. It is therefore usually desirable to position the antenna elements far apart within a device and/or to use radiofrequency (RF) shielding therebetween while balancing its size and other design constraints.
In particular, most of the existing decoupling techniques suitable for mobile terminals focus on relatively high frequency bands, including the WLAN, DCS1800 and UMTS bands, whereas the isolation for low frequency bands below 1.0 GHz is typically worse than 6.0 dB. For low frequency bands, the chassi plays an important role in determining the mutual coupling among the antennas, since the chassis not only acts as a ground plane, but also as a radiator shared by the multiple antennas. Thus, the radiation patterns are modified by the chassi, so that the angle and polarization diversities are difficult to achieve. As a result, the achievable performance of the multiple antenna terminals in MIMO applications may be degraded.